That's true. I've used some pretty good finders, but they are still dependent on the lens speed. I'm happy with my 35 f2.8 Distagon, but not with focusing it indoors. With a Leica, or similar, that isn't a factor.
I agree that SLRs can provide a struggle with focus in low light, the advantage for the rangefinder here lies in the body/rangefinder mechanism not being affected by the lens brightness, right?
Mark Barendt, Ignacio, CO
"The mind that opens to a new idea never returns to its original size." Albert Einstein